1 - Bilsteins.
2 - Boge, if you can't afford the Bilsteins.
3 - Koni.  I have not used them on a Vanagon, but I have never been
diappointed with them on any other wheeled appliance.
4 - KYB, if you don't mind a harsh ride, spooky handling and changing them in
about a month.
5 - ALKO makes trailer suspension components.  Enough said.

George